1. Field of the Invention
This invention relates generally to transmissions for varying the speed and torque ratio between an input driving member to which mechanical energy is applied and an output driven member. More particularly the invention is an entirely mechanical transmission mechanism, which automatically and continuously varies the transmission ratio in a stepless manner as a function of input and output torque and speed. Although the transmission is particularly suitable for bicycles, it also has properties which are advantageous for other vehicles and other machines.
2. Description of the Related Art
There are numerous transmissions in the prior art for interposition in the drive train of vehicles and other machines so that the drive ratio can be varied in order that a prime mover can operate over its operating torque and speed range while permitting the output to vary over different and usually considerably broader torque and speed ranges needed during various anticipated modes of operation. Initially, transmissions were manually operated to select one of several discrete transmission ratios. Bicycles typically use derailleur systems or gear transmission in which selected different sprockets or gears are alternatively engaged to select from the available ratios.
The prior art recognized that ease and convenience would be enhanced if the vehicle operator were relieved of the responsibility for deciding which transmission ratios would be appropriate for the encountered conditions and for manually shifting the transmission. Consequently, there have been a variety of automatic transmissions. Some of these are based upon the automation of a manual transmission using speed or torque sensing devices. Some shift between discrete gear engagement choices while others use belt and pulley systems which vary the effective pulley diameter. Still others are hydraulic systems which use hydraulic pumps, motors and valving arrangements.
Such prior art transmission systems, although they accomplish the necessary drive ratio changes, are complicated, and therefore expensive, devices which are consequently subject to several modes of failure. Some such systems shift abruptly or in a stepped manner between discrete ratios instead of in a smoothly continuous manner.
It is therefore an object and feature of the invention to provide an automatic transmission which is both simple in its construction, requiring few parts, and which may be entirely mechanical, making it particularly suitable for bicycles.
A further object and feature of the invention is to provide a transmission which progressively varies its drive ratio in a smoothly continuous manner in response to variations in load power demand and input power.
A further object and feature of the invention is to provide a transmission which is particularly suitable for a bicycle and allows a rider to pedal at the rider's comfortable pedal speed and torque while the transmission automatically varies the drive ratio in response to load power demand, such as caused by inclined surfaces, without causing substantial variations in the input torque and speed perceived by or required by the rider.
A further object and feature of the invention is to provide, in combination with one or more of the above features, a transmission which also allows the rider to pedal faster or slower to accelerate or decelerate without experiencing substantial pedal torque variations so that the rider perceives a response from the pedal effort which is similar to that given by a conventional bicycle.
Yet another object and feature of the invention is to provide a transmission which can be adapted to drive multiple wheels on a vehicle and allow the wheels to turn at different speeds so that the transmission also provides a differential function and applies drive torque to all wheels, including a nonrotating wheel.
Another object of this invention is to provide a transmission that can drive the same shaft at different torque ratios, as for example, on a bicycle, a linkage on one side of the wheel can drive preferably at low speeds and high torque, and another linkage, driven from the same driving crankshaft, can drive the same wheel more optimally at a higher speed and lower torque, but at any instant, both sides are driving the wheel at the same speed. This feature can be extended so that a single driving shaft can drive any number of different driven shafts simultaneously at different speeds and or torques, or, can drive a single driven shaft with any number of linkages having different torque-speed characteristics.